1. Field of the Invention
This invention relates in general to the field of Radio Frequency Interference (RFI) and Communications Electronic Warfare (EW). More particularly, this invention relates to automated interactive adaptive antenna patterning apparatus, methods and computer programs for modeling and evaluating performance of adaptive null steering antenna systems considered to be operating in the presence of a given number of interference sources.
2. Description of the Prior Art
Adaptive array antennas, interference cancelers and side-lobe cancelers produce different antenna patterns in different electromagnetic environments. In the past, it has been difficult to evaluate the requirements for, or performance of, antenna and processor systems without a specific model of a particular system. Generally, antenna models are limited to single applications, complicated and costly to develop and do not have sufficient flexibility needed for design engineering studies. For example, an engineer could not use previous models to determine whether additional or fewer nulls would be effective in a design. Understanding antenna patterns is particularly important in the area of electronic countermeasures and jamming.
To predict the performance of adaptive array antennas, the antenna's pattern must be determined, which depends on factors such as the antenna's physical characteristics and the number of independent incoming RF signals that the antenna "sees." A resulting Signal-to-Noise ratio (S/N) must also be calculated. Furthermore, currently available antenna models have to be embedded in a scenario model in order to truly reflect system performance and require the operator to evaluate one link at a time. Prior art antenna models suffer from the drawbacks and limitations of being too specific or unique, and being unable to determine optimum null quantity limited to one link at a time.
Those concerned with the antenna performance and design parameters have long recognized the need for an economical and flexible means of evaluating the performance of the adaptive array antenna. This would allow the designer to define the expected environment, have the flexibility needed for design engineering studies, do cost trade-off analyses and accurately predict the formation of the antenna pattern under different conditions and scenarios.
The present invention fulfills those long-recognized needs without suffering from the drawbacks, disadvantages and limitations of prior art antenna models by providing automated interactive adaptive antenna patterning apparatus, methods and computer programs which better predict adaptive array antennas' behavior, allowing the designer to inexpensively and economically utilize numerous adaptive array antenna characteristics and many scenarios as data inputs, without requiring costly single application models. The present invention allows a designer to evaluate the optimum number of nulls in a given scenario and to determine if using unengaged tracking loops to maximize the desired signal provides improved performance. Not only does the present invention overcome the drawbacks and disadvantages of prior art antenna models, it also provides both superior fidelity in modeling Graham-Schmidt processors by not canceling prior nulls and the additional flexibility of defining the upper limits of null depths rather than assuming a fixed percentage of canceled capability. The preferred embodiment of the apparatus and an article of manufacture of the present invention, provides a computer program known as the Jammer Scenario Effects Assessment Model (JAMSEAM).
In general, the adaptive antenna patterning apparatus of the present invention, contemplates an antenna modeling means building an adaptive antenna description, representing a number of antenna elements, a means for determining angle-of-arrival, a means for rank-ordering, a means for sorting, a means for antenna patterning and a data output means that provides a composite antenna pattern for each of the array's receivers. The adaptive antenna patterning apparatus can better determine adaptive null steering antenna patterns produced in the presence of numerous interference sources.
In general, the methods of the present invention, encompass the steps of forming an adaptive antenna description, determining angle-of-arrival, rank-ordering interference peaks, building a nulling table in a sorting means, calculating a total interference signal level and a signal to noise ratio plus interference ratio for each of the array's receivers, forming an antenna pattern at the receivers, applying each pattern to determine nulled interference signal-to-noise level at each receiver and providing a data output means with the composite antenna pattern for each receiver. The computer program disclosed and claimed as an article of manufacture operates in a manner similar to the apparatus.
In addition to analyses of adaptive array antennas, the apparatus, methods and computer programs of the present invention would be extremely useful to predict the behavior of interference cancelers, side-lobe cancelers and single element antennas in various signal environments. Potential uses include predicting performance of potential enhancement antennas for the Mobile Subscriber Equipment (MSE) and other military applications, as well as designing new antennas, evaluating the use of existing antennas in specific customer applications, antenna performance evaluation, network planning, antenna enhancement trade-off analyses, signal interference assessment and battlefield survivability.
General references in the field of antenna performance analysis include:
Torrieri, Donald J., Principle of Secure Communications, Norwood, Mass., Artech House, 1985; and PA0 Jordan, Edward C., Electromagnetic Waves and Radiating Systems, New York, Prentice-Hall, 1950. PA0 Gabriel, William F., "Adaptive Arrays--An Introduction", 64 Proceedings of (IEEE), Number 2, pp. 239-272, February 1976. PA0 "Using Spectral Estimation Techniques in Adaptive Processing Antenna Systems," IEEE Transactions on Antennas and Propagation, Volume AP-34, Number 3, March 1986.
Examples of adaptive array antenna processors may be found in the following references: